Wireshark is the most popular network troubleshooting tool - protocol analyzer as they call themselves. It is free and open source. It can be used for network analysis, troubleshooting, protocol analysis and education.
Website: https://www.wireshark.org/
Microsoft Network Monitor is another tool which can be used for network troubleshooting. An important feature of Microsoft Network Monitor is you can see which process is sending or receiving which packets.
Website: https://www.microsoft.com/en-us/download/details.aspx?id=4865
Fiddler is a network debugging tool. Unlike Wireshark and Fiddler, you can not see the packet details. It is helpful showing all the details of http connections. By importing the ssl certificate to fiddler, you can decrypt, view, and modify HTTPS-secured traffic for debugging purposes.
Website: http://www.telerik.com/fiddler